You can try PAL, or Philippine Airlines out of LAX or SFO directly to Manila. They fly a 747. Probably cost you around 80 bucks each way on an ID 90 or ZED.
Also, I think SFO or LAX is better than IAH because its closer to Manila than from Houston. I don't know of any direct flights IAH to MNL, but I do know there is a direct LAX/SFO to MNL via PAL.